Consider a vent in each end of your garage/paint booth, framed in to accept a furnace filter. Put your fan outside the paint booth, blowing air thru the filter into the paint booth. It will work best if you build a shroud (as in the 1/2 oil drum with both ends cut out, so that the air from the fan must go thru the filter into the spray booth). The positive air pressure created inside the spray booth will cause an equal airflow thru the filter at the other end, carrying the paint fumes with it, and there is nothing at that end to create a spark.---why put a furnace filter at the other end?---to keep the mosquitoes and houseflies from coming into the booth.